A cement is a mineral powder designed to be mixed with water in order to form a cementitious composition with a pasty or liquid consistency that hardens in order to form a hardened final material.
There are many cements on the market that can be distinguished, on the one hand, by their reactive properties with water, and on the other hand, by the mechanical and chemical properties of the hardened final materials that can be obtained from them.
For example, calcium aluminate cements provide the hardened final materials with specific chemical properties of high resistance to acid corrosion and mechanical properties of high resistance to high temperatures and pressures.
The reactive properties of a cement when it is mixed with water determine the workability of
the cementitious composition formed by the mixture of this cement with water, i.e. the duration, also called “open time”, during which this cementitious composition has a viscosity adapted to its use, namely, for example, a low viscosity in order to allow the injection thereof into cracks, or a moderate viscosity in order to allow for the shaping thereof in formworks.
These reactive properties also determine the hardening kinetics of the cementitious composition during later phases of the reaction of the cement with the water. These are in particular the characteristics of the hydraulic setting of the cementitious composition, with the hydraulic setting being an accelerated exothermic phase of the hydration reaction of the cement by the water, and of the speed at which the final hardening of the material occurs after the hydraulic setting, namely in how much time the hardened final material reaches a desired mechanical resistance.
Furthermore, it is known that a relatively high temperature, i.e. greater than about 50° C., even greater than 30° C., can accelerate the hardening kinetics of a cementitious composition, and substantially reduce its workability in particular by favouring the thickening of the cementitious composition and by triggering the hydraulic setting faster.
In order to decrease the effect of the temperature on the reactivity of the cementitious compositions, it is common to add adjuvants to the cementitious compositions, such as setting retarders.
However, as several retarders can be used in the same cementitious composition, these retarders can interact together and/or with the other additives of the cementitious composition, and it then becomes difficult to predict the hardening kinetics of this cementitious composition.
In addition, the presence of a retarder in the cementitious composition can lead to a lowering of the mechanical resistance of the hardened final material.
Moreover, it is also known that, due to these problems of workability and of hardening kinetics, cementitious compositions with a calcium aluminate base are generally manufactured on site, i.e. the water is added to the cement directly on the location of use of the cementitious compositions.
It is as such a regular occurrence that, on site, cementitious compositions with a base of calcium aluminate cements are prepared in production lines that are normally used to prepare cementitious compositions with a base of Portland cement.
As production lines comprise dead zones that are difficult to purge and/or to clean, a small amount of cement may remain from one production campaign to another. As such, during the preparation of a cementitious composition with a Portland cement base, it occurs that this Portland cement has been polluted by remainders of calcium aluminate cement, or inversely.
Yet, Portland cements and calcium aluminate cements interact with each other, and this interaction accelerates the hardening kinetics of the cementitious compositions obtained. As such, the hydraulic setting of a cementitious composition with a base of a mixture of Portland cement and of calcium aluminate cement is initiated earlier than what is expected for a cementitious composition with a base of Portland cement or of calcium aluminate cement only. When this mixture results from an involuntary pollution, the acceleration in the setting can result in blocking the installations, which is very problematic.
An application wherein generally high temperatures are involved, and for which it is essential to control the workability and the hardening kinetics of the cementitious compositions formed is the consolidating of drilling wells.
Drilling wells, and in particular oil wells, is a complex process that consists mainly in drilling the rock while introducing therein a tubular metal body.
It is known to cement the walls of drilling wells in order to reinforce the formwork of these wells and to protect the tubular body that is inserted therein from corrosion, as well as to seal this tubular body in the neighbouring rock.
To do this, industrialists use cementitious compositions in the form of aqueous suspensions commonly referred to as slurry, mainly comprising a cement, possibly aggregates or specific cementitious additions, dispersed in a relatively large quantity of water, that they inject into the tubular body to the bottom of the latter. The aqueous suspension then rises to the surface, in the space that exists between the rock wall and the tubular body.
It is then understood that the workability of the aqueous suspension must be such that this aqueous suspension can be injected to the bottom of the tubular body, and that the hydraulic setting of the aqueous suspension must occur at a controlled moment after the rising to the surface of this aqueous suspension, and this taking the underground conditions of high temperatures and pressures into account.
It is known for example from document US20130299170 complex cementitious compositions in the form of aqueous suspensions, suited for the consolidating of oil drilling wells, that include calcium aluminate cements and setting retarders comprising an organic acid and a mixture of polymers.
It is also known from documents U.S. Pat. No. 6,143,069 and US20040255822 cementitious compositions in the form of an aqueous suspension with a low density, suited for the consolidating of oil drilling wells, comprising a commercial calcium aluminate, of the brand SECAR-60™ or REFCON™, fly ash, water, retarders such as citric, gluconic or tartaric acids and other additives such as foaming agents and agents that prevent the loss of fluid.
However, the cementitious compositions formulated as such to reduce the effect of the temperature on their workability and their hardening kinetics are particularly complex. They moreover result in the use of many different chemical compounds, which can have a harmful effect on the environment.
There is therefore a need to be able to benefit from the properties provided by the hydration of calcium aluminates while still more easily controlling the period of workability in particular when the temperature is high, and tolerating a certain pollution by Portland cements or in Portland cements.